Compressing converter for translating analog signal samples into pulse code modulation signals

ABSTRACT

A device for converting analog signal samples into PCM signals, comprising means for successively comparing to a predetermined reference voltage the amplitude of each sample and the successive products thereof by increasing powers of two. At each comparison showing said amplitude of one of said products to be smaller than said reference voltage, a binary digit of a given signalling condition is generated, while a binary digit of the other signalling condition is generated as soon as a comparison shows one of said products to exceed said reference voltage. A remainder signal derived from the latter comparison is transmitted to a linear PCM coder, which delivers a first sequence of PCM signals, while a computer translates the sequence formed by the above-said digits into a second sequence of PCM signals. The assembly of both sequences constitutes the ready-tobe-transmitted PCM signal groups. The device is further characterized in that it makes use, for the successive comparisons, of a plurality of cascaded circuits, each of which includes a difference amplifier with two negative feedback paths, one including a diode having its conduction direction from the output to the input of the amplifier and series connected with a resistance, and the other including a diode having the reverse conduction direction and series-connected with another resistance equal to half or twice the preceding one according to the even or odd rank of the amplifier in the cascade. Thanks to this arrangement, the difference signal resulting from each comparison is multiplied by 1 or 2 according to its polarity, this allowing to use a common reference voltage for all stages of the cascade.

United States Patent [151 3,653,032

Le Fort [45] Mar. 28, 1972 [s41 COMPRESSING CONVERTER FOR [57] ABSTRACT TRANSLATING ANALOG SIGNAL A device for convening analog signal samples into PCM SAMPLES INTO PULS CO signals, comprising means for successively comparing to a MODULATION SIGNALS predetermined reference voltage the amplitude of each sample and the successive products thereof by increasing powers Inventor: f' For! 28 Corlay, of two. At each comparison showing said amplitude of one of Lanmon Franc" said products to be smaller than said reference voltage, a bi- [22] Filed: Oct 20, 1970 nary digit of a given signalling condition is generated, while a binary digit of the other signalling condition is generated as [21] App]. No.: 82,420 soon as a comparison shows one of said products to exceed said reference voltage. A remainder signal derived from the latter comparison is transmitted to a linear PCM coder, which [30] Foreign Appnuflqn Priority delivers a first sequence of PCM signals, while a computer Oct. 29, 1969 France ..693720l translates the sequence formed by the above-said digits into a second sequence of PCM signals. The assembly of both [52] us. Cl ..340/347 AD q ence constitutes the ready-to-be-transmitted PCM signal [51] Im.Cl H03k 13/06 groups. The device is further characterized in that it makes [58] Field of Search ..340/347 AD use, for the successive mp of a pl r li y of cascaded circuits, each of which includes a difference amplifier with l 56] R f e Cited two negative feedback paths, one including a diode having its conduction direction from the output to the input of the am- UNITED STATES PATENTS plifier and series connected with a resistance, and the other ineluding a diode having the reverse conduction direction and g lzfi series-connected with another resistance equal to half or twice o u I l n s e e s a u e a u s I s u a I et k f 3,444,550 5/1969 Paulus ..340 347 AD precedmg acwdmg to he even 0 ran 0 e Primary Examiner-Maynard R. Wilbur Assistant Examiner- Robert F. Gnuse AttorneyAbraham A. Saffitz amplifier in the cascade. Thanks to this arrangement, the difference signal resulting from each comparison is multiplied by 1 or 2 according to its polarity, this allowing to use a common reference voltage for all stages of the cascade.

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PATENTED MR 2 8 I972 SHEET 3 UP 5 INVENTOR: Gilbert J. LE F0 T ATTORN PATENTEDMAR28 I972 3,653,032

S iEET []F 5 INVENTOR:

Gilbert J. LE F RT ATTO ANALOG SIGNAL SAMPLES INTO PULSE CODE MODULATION SIGNALS This invention relates in general to PCM (pulse code modulation) communication systems, more particularly to converters for translating repetitious amplitude samples of analog signals into coded groups of binary digits, the encoding being accompanied by amplitude compression of the sample. a

More particularly, the'encoder according to the invention belongs to that category of compression encoders inwhich the sample is first translated without compression into .a first group of binary digits whose value is expressed in one particular code, whereafter the first group of binary digits is'translated in a system of logic circuits into a second group of binary digits expressing the binary-code value of the sample.

The normally used compression pattern in connection with the translation of analog signals into PCM signals is given by y= oset +1 g( +1) in in which y p /N and x V,,/V,,,,,,.; p denotes the quantized level rank counted in the sense of increasing amplitude; N 2" the total number of quantized levels; V, denotes that value of the amplitude of the sample .to be encoded which is applied to the encoder input for'the level of rank p; V denotes the maximum voltage which the encoder can process; and denotes a dimensionless parameter with an optimum value of 100. The encoder according to the invention keeps approxi-v mately to thie pattern in that the quantification level width Ax corresponding to a constant height Ay l of the step does not vary continuously with x but remains constant over certain ranges of x. The principle underlying this kind of encoding'is described in detail in Robert Mauduech's French Pat. specification No. 1,593,017 of 1 1 Sept. 1968.

The transmission code used is a seven-digit binary code in which the first digit S denotes the sign, the next three digits ABC denote the binary number of one range of amplitudes of a total of eight, in which range the width of the quantized levels is constant, and the last three digits XYZ denote the binary number of the quantized level in the range. The part ABC corresponds to a "nonlinear encoding and the part X YZ corresponds toalinear encoding. a 1

' Leaving aside the. binary sign digit, the encoding table is as follows:

TABLE 1 xvz V g g 1 s 000 001 010 on too m1 110 111 ABC v 000 o 1 2 s 4 s s 7 001 s 9 1o 11 12 1s 14 1s 0l0 1s 1s 20 12 24 26 as so 011 :42 as 4o 44 4a 52 so '60 100 64 72 so as '96 104 112 120 101 us 144 160 m 192 ms 224 240 110 25s zas 320 as: 334 41s 4411 430 111 st: 576 640 104 768 as: 1196' 960 The Table shows that the value of the quantized level in the range and the width of the range increase as powers of two except for the first line corresponding to ABC 0.

The encoder first translates the sample into a number containing eleven binary digits d d ,...d of which the first digit d is equal to the binary sign digit, the next seven digits (1: to d, are expressed in the particular code hereinbefore mentioned and are correlated to the three binary digits ABC, and the last three d,, d,,,, d are expressed in the Gray'code, also known as the reflected binary code, and are correlated to the three binary digits X YZ.

The code for expressing the number (11,, d,,...d,,) is a code in which the 0's and 1's can never be interlaced and in which the number of different 1's in the encoded group is equal to the decimal number equal to ABC. For instance, if ABC l l l 7, then:

d,d,d,d,d,d d, 1111111 i.e., the encoded group contains TABLE 11 d2 d3 d4 (is do (11 da A B C Hence:

=da+ 1 s t3) z+ 3 t'i' s la-F 1 s' As previously stated, the number (do, dm, dn) 1s expressed in-the Gray code, the translation table being as follows: I

the actual encoder, the system of logic circuits deduces A, B,

The encoder comprises elementary translators known in the prior art. An elementary translator is v a circuit having one analog input and three outputs, one of which is digital and the other twoof which are analog. According as the input signal is negative or positive, the signal at the first output is a digital signal of onevor the other polarity. When the input signal varies from negative to positive, the signal at the second output is to start with'proportionalto the. input signal in the negative part thereof, then 0 in the positive part of the input signal, and the signal at the third output is 0 to start with the negative part of the input signal, then proportional thereto in the positive part thereof. If a substraction of the signals of the two analog outputs is made, the transfer characteristic -i.e., the relationship between the amplitude of the input signal on the abscissa and the amplitude of the output signal on the ordinate has the shape of a V whose apex is at the origin and whose bisector is the axis of the output signals. If a reference signal is added to the input, the. apex of the V can be shifted along the output signal axis. Circuits of this kind are known in the prior art and are described'e.g., in US. Pat. specification No. 3,145,377 of 18 Aug. 1964 and French Pat. specification No. 1,367,773 of 2 July, 1963. Their construction will be recalled in detail hereinafter.

These translator .circuits can compare an analog sample voltage or input voltage with a reference voltage. and produce a signal when the input voltage is greater than the reference voltage, giving 0 signal when the input voltage is smaller than the reference voltage (or vice versa). They also make it possible to. produce a remainder voltage equal to the reference voltage less one or more times the input voltage.

The input voltage is therefore compared seriatim with reference voltages 8, 16, 32, 64, 128, 256, 512 in translator stages. The translator outputs a l or a 0 (or vice versa) according as the input voltage is above or below the translator reference voltage, so that the digits'd, to 11,, are produced consecutively. If the input voltage is below the reference voltage, a further comparison is made, this time between the same reference voltage and twice the sample; a remainder is transmitted to the next stage and no remainder is transmitted to the linear encoder supplying (d d d If the input voltage is above the reference voltage, no remainder goes to the next stage and a remainder goes to the linear encoder outputting wand").

For instance, if the sample has the value 88, it is compared with 512; since the sample is smaller than 512, d 0 is deduced and 2(5 12-88) -i.e., 2 X 88 is then compared with 512; since the answer is smaller than 512, (l is taken to be 0, 2(512 2 (51288)) is transmitted to the next stage and nothing is transmitted to the linear encoder. This term is compared with 512, which comes to comparing 4 X 88 with 512. Since it is smaller, d is taken to be 0, and in the next stage 8 X 88 is larger than 512, d, is taken to be 1; nothing goes to the next stage and (5 l2-8X88) goes to the linear encoder.

As a result of the encoding procedure described, all translators have the same either positive or negative reference voltage a considerable simplification and the remainder for linear encoding always goes to the linear encoder with con-' stant levels, whatever the amplitude range in which anyremainder has been found. This constant level is the level of the amplitude range ABC l l l and has a value of 64 units; in the example given the remainder for linear encoding is found in the amplitude range ABC I in which the level hasa value of 8 units, but it is transmitted multiplied by 8; this latter, feature makes it possible to add the remainders and give them a single linear encoding.

The invention will now be described in detail with reference to the accompanying drawings, wherein: 1

FIG. 1 shows an elementary prior art translator, illustrating; how it has been modified for the purposes of this invention;

FIGS. 2A and 2B show the encoder according to the inven-- tion, the computer part being shown in block diagrammatic form;

FIG. 3 shows the encoder computer;

FIG. 4 is a diagram helping to explain how the encoder operates;

FIG. 5 is a second diagram helping to explain how the en-' coder operates, and

FIGS. 6 and 7 are explanatory diagrams related to a variant of the invention.

A modified prior art translator circuit is shown in FIG. 1, where there can be seen an operational amplifier having a high input impedance, a low output impedance and a high voltage gain and a high current gain. The voltage at input terminal 5 of amplifier 20 is therefore substantially ground potential. The noninverting amplifier input is grounded and the inverting input 5 is connected to the analog signal input terminal via a resistance 2 and to a terminal 3 which receives a reference current via a resistance 4. The reference current determines the reference voltage at which the comparison is[ made. The amplifier has two negative feedback paths, the first? path comprising a diode 6 and resistance 8and the second path comprising a diode 7 and resistance 9. The diodes 6 and 7 are connected the opposite way round in their respective negative feedback paths.

The translator circuit has three output terminals 1012.; Terminal 10 is the digital output which outputs the required:

binary digit 11,. Terminals 11 and 12 deliver the remainders which go either to the next stage or to the linear encoder. In the prior art elementary translators the remainder was equal to the reference voltage serving for the comparison, less half the input voltage, as a result of an appropriate choice of relationship between the joint value of the resistances 8, 9 and the 6 value of the resistance 2, the latter being twice the former.

In translators according to the invention, there are two remainders, one of which is equal to the reference voltage less the input voltage and the other of which is equal to twice the reference voltage less the input voltage. This is achieved by' taking:

Value of 9 R Value of 2 R Value of 8 R Value of 9 R or depending upon which terminal, 11 or 12, it is desired to connect to the next stage and the the linear encoder, i.e., delpending upon the polarities of the signals delivered at these iterminals.

When the current at input 1 is greater than the current at input 3, the total input current is positive and the voltage at output 10 is negative. Diode 6 is biased backwards. Consequently, no current flows through resistance 8 and the output voltage at 11 is equal to the input voltage i.e., 0. If the current at the input I is smaller than the current at the input 3, the total input current is negative and the voltage at output 10 {is positive. Diode 6 is biased forwards and the output terminal @11 goes positive. The value of the voltage thereat is 2(V,,, .ere nre 'lnpur) if R8 2R2, nelerence lnpur if R8 R2- This is the voltage shown beside terminal 11 in FIG. 1. The nature of the voltage E shown beside terminal 12 can be worked out' in the same way. The curves representing voltages E 5,, together form a V having one steep side (slope 2) and another less steep side (slope 1).

The encoder according to the invention, which is shown in FIG. 2, comprises stages 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500. Except for the stages 700, 1000, 1500, which are ordinary amplifiers, all the other stages are translators of the kind shown in FIG. I. The constituent elements of the various stages have the same reference numbers in FIG. 2 as in FIG. 1 but preceded by a hundreds number which is the same as the hundreds number .of the reference number for the particular'stage concerned.

Stage is an input stage which delivers to stage 200 a sample, the samealways being of the same polarity. In addition to the conventional parts of the elementary translator, Stage 100 comprises a chain of two resistances 115, 116 con- 'nected between output terminal 111 and input terminal 101.

[1 he output of stage 100 is a point 119 common to the two resistances 115, 116. If the input voltage applied between the terminals 101 and 101 is negative and equal to V, the volt- }age at output terminal 111 is 2V (the diode 116 is conductive). Since input 205 of stage 200 is always virtually at ground potential and has a high impedance, the voltage applied to input 205 can be considered to be proportional to the sum of the currents which flow through the resistances connected to it. This sum is 2V/R (through 115) V/R (through 116) V,,/R,, (through 204) V, denoting the potential of bus-bar 3, so that we have When the input voltage is +V, the voltage at output terminal 111 is 0 and the current applied to input 205 is V/R (through 116) V,,/R (through 204).

The same expression is found, and the input signal polarity of stage 200 is the same whatever the input signal polarity of stage 100.

The biasing stages 200,300, is taken from a negative bus-bar 3 through the resistances 204, 304,

504 and the biasing current for the stages 400, 600 is derived from the positive bus-line 3' through the resistances 404 and Outputs 210, 310, 410, 510, 610 deliver the binary digits (1:, 1d}, (1,, d1, d, respectively. Cascading is via resistance 23 from ioutput 211 to input 305, via resistance 34 from output 312 to input 405, via resistance 45 from output 411 to input 505 and via resistance 56 from output 512 to input 605. The interconnectionsare of course alternately by way of one and the other of the two outputs of each translator. All the interconnection resistances have the same value R. Those outputs of each translator which are not used for cascading i.e., outputs 212, 211, 412, 511, 612 are connected via resistances 213, 313,

513, 613 to an addition rail 14.

described. Its function is to ensure The channel of stages 1100, 1200, -1300; 1z00T150Ts for Stage 1100 has anoperational amplifier 1120'with negative feedback paths. The first path comprises a biasing} source 1116, a diode '1106 and a resistance 1108, the diodei conducting from output 1110 towards input 1105; The secondf path comprises a biasing source1117,diode 1107 and resistance 1109, the diode 1107 being conductive from input} 1105 to output 1110. The third path comprises'a rectifierl bridge 1115.and a resistance..1l18. The rectifier br'idge 1115; is energized by currant supplies 1121, 1122 through resistances 1123, 1134. The supplies 1116, 1117 have a voltage;- V. The sample to be encoded is applied to the input of amplifier 1120 through resistance 1102. When the output voltage between V, and +V,, V correspondsto 32 levels and third branch is operative. When theoutput voltage is above! 1,611 and 1,612, which deliver d,

V the first branch is operative, and when the output voltagei is below V the second branch is operative. FIG. 5 represents the voltages at the points 1111, 1112 andf 1119. The chain of circuits comprising the stages 1200, 1300,! 1400, 1500 is energized by the voltage at the point-1 119. 3

The stage 1200 is identical to stage 100 and need not be; that the input signal for} stage'1300 is alwayspositive. l v e j The stages 1300 and 1400 areidentical to the stages 300i and 400 respectively; they are interconnected by resistance. 1314 between output terminal 1312 and input terminal 1405; their input terminals are connected to rail 3 by resistances} 1304 and 1404, and their output'terminals 1311 and 1412 are T connected'to the additionrail 14, by resistances 1313 and 1413. Their output terminals 1-310, 1410 deliver signals d, and sqrss flrelyt a f drdinaryiunity-gain inverter 1520i Stage 1500 comprises an whose input-terminal .1505 is connected to output terminali 1411 of stage 1400 via resistance 1415 and whose output ter-. minal 1510 is connected to addition rail 14 by resistance 1 51 3 .f

7 FIG. isi a graph toillustrate the operation of the nonlinear encoder, disregarding thecomputer which will be dealt withi subsequently. The input voltage is plotted along the abscissa; the scaleis linear between 0 and 16 (and between 0 and 16 and logarithmicbetween 16 and 960 (and between -16 and] .-960). The voltage 512 is compared with the sample 88, then! with twice the sample L i.e., with 176 then with four times thei sample -3 52 then with eight times the sample 704. The first| three comparisons give d d; d, 0; the fourth gives d Li and since 1 sans! hsjssassstksiaerlasse we e;

The linear encoder comprises the stages 700, 8 00, 900,

1000. Stage 700 is an additionamplifier whose input is con- 1 nected to the addition .rail 14. Stages 800 and 900 are of the same construction as stage 100. A point 819 common to the two resistances 815 and 816 is connectedto input terminal 905. Also, the point common to the resistances 915 and 916'is connected to input terminal 1005. The resistance 816 also performs the function of the resistance 102. The outputs 810, 910, 1010 deliver the binary digits d d d respectively.

The values of 804, 904, 1004are as follows 25.6 for 804; 256 l28'= 384 for 904;

and 256 128 64 448 for 1004. They areconnected to;

thesame negative potential source.

following values of X, Yand Z FIG. 3 shows the' logic ci'rcuit 1,600 of FIG. 2 which i' i s uds. 5. 6. 1. w n d" a al a s formulas 1(3) and (4). S is equal to 1 A is equal tad B is ob- ;tained by the inverter1602 which gives d,, by the inverter, 1,603 which givesdby the-AND-gate 1,604 which givesd. d,, and by OR-gate 1605which gives d; d 11,. C is obtained ;by AND-gates'1,606-1608, giving d, d d, d, and d, d, respectively, and. by OR-gate 1619, whichv summates these three products and d,. X is equal to d 1,609 and 1,610,

which deliver d a nd d by AND-gates g'ate 1,613, which summates thesetwo products. 2 is obtrgned by the inverters 1614 and 1615, which deliver d and Y, by

AND-gates 1616 and 1617, which deliver Yr? and Yd and by OR-gate 1618, which adds these two products.

responding to the channel consisting of the supply 11 16, diode 1106 and resistance HOS-previously seen in FIG. '2, and one ;of the paths starting from supply 2117 is, merelythe path previously seen inFIG. 2 and comprising the supply 1117, diode 1107 and resistance 1109, The other path starting from ithe-supply 2116 comprises diodes 2104, 2106 and a resistance I 2108, and the other path starting from supplyv 2117 comprises 2110 and 1 idiodes 2105, 2107 is grounded via .supply 2115,

idiodes 2105, 2107 and a resistance 2 {between the two diodes 2104, 2106is grounded via resistance power supply 2114. The comm on pointto'the two resistance 2113 and power The signals at'the points 1119, 1111', 2111, E1112, 2112-are summated by adding resistances 2151-2155, iall of the same value, and applied to the input of amplifier 52120.

' In normal conditions a current flows through the path formed by the'supply 2115, resistance 2113, diode 2107, re.-

'- isistance2-109, resistance 2109, diode '2106, resistance 21:10

land supply 21-14. The supplies 2116, 2117 are identical so that ithe diodes 2104, 2105 are'nonconductive. For low-amplitude signals the stage-shown in FIG. 6 behaves isimilarly to the stage 1100; when the output signal increases,

{for instance, in a positive-going sense, and exceeds lnlhrl,

idiode 2104 passes a current which returns to supply 2114 ithrough resistance 2110 and which alters the current flowing gthrough resistance 2108 Because of this variation of the curirentfiowing therethrough, the potential of the point 2111 vasries in proportion to the voltage applied to input l01.-The !variation of the potential of the point 2111 (part b of the dia- Egram in FIG. 7) is also proportional to the relationship Ram/R 02; If the'potential of output terminal 1110 continues,

' to rise and exceeds Vilma/2, the current output by'squrge 52108 is inoperative, being replaced by resistance 1108 since the voltage at terminal is high enough to make conductive the diode 1106 previously kept nonconductive by the supply 1116. The point 1111 rises to a potential determined'by the current flowing through the resistance 1108 (part c of the diagram in FIG. 7). 1

As the voltage at output terminal 1110 increases, the various variations of the points 1119, 21 1 1 and 1111 are amplified consecutively in the amplifier 2120, the resistances 2151, 2152, 2153 being respectively and consecutively connected thereto because of the current variations which they are Y is obtained by the inverters d respectively, and by OR- 109. The common point I {2114 is completely absorbed by diode 2104 and the resistance required to transmit. The gain of amplifier 2120 is adjusted by resistance 2128.

Negative variations of the potential of point 1110 are treated symmetrically by like circuits of the other branches and the transfer characteristic of a system of this kind is given in H6. 7. Such characteristic takes the form of a curve consisting of line-segments whose slopes are determined by the ratios of the resistances 1118, 2108, 1108, 2109 and 1109 to the resistance 1102. In the present case the ratio of the consecutive slopes is 1 2 but this value is not restrictive and can be varied just by changing a resista n ce.

The number of line-segments is not limitative .either; if circuits similar to those embodied by the integers 2108, 2106,

2104 and 2109, 2107 and 2105 and the supplies 2114, 2115 and the resistances 2110, 2113 are added to the circuit arrangement shown in FIG. 6, two further segments can be provided. This feature forms a compressor which can be associated with an encoder of the kind constructed from the stages 800, 900, 1000 of FIG. 2 with an increased number of; s- 152f swaths! swskis f ss sn sqsn This circuit can also be associated with a known kind of encoder to act as an expander. In this event, the values of the resistances 1118, 2108, 2109 and 1109 and of the power supplies 1020,- 1030, 1021, 1031 must be modified to give a characteristic which is the reverse of the characteristic shown in FIG. 7 and which is shown therein in broken lines.

lclaim:

1. A device for convening analog signal voltage samples into PCM signals with amplitude compression, comprising:

means for successively comparing with a predetermined reference voltage each of said samples and the products thereof by increasing powers of two and for producing from the comparison an encoded binary sequence con-' sisting of binary digits having one predetermined of two possible signalling conditions each time said voltage sample and products are below said reference voltage;

means for forming remainder signal whose amplitude is, equal to the difference obtained by subtracting said reference voltage from the lowest of said products which is larger than said reference voltage;

a linear encoder for linearity encoding said remainder signal and translating it into a first PCM coded group;

fl ac omputer for translating said sequence into a second PCM coded group;

and means for transmitting the assembly of said first and second coded groups;

said device being further characterized in that:

said successive comparison means and remainder signal forming means consist of a plurality of cascaded circuits, each of which comprises a differential amplifier having a first and a second negative feedback path, said first negative feedback path including a first diode oriented to conduct from the output to the input of said amplifier and se ries-connected at a first common point with a first resistor, said second negative feedback path including a second diode oriented to conduct from the input to the output of said amplifier and series-connected at a second common point with a second resistor having either of two resistance values equal to half and twice that of said first resistor according to the even or odd rank of said amplifier in said plurality of cascaded circuits whereby said amplifier delivers at one or the other of said common points a voltage equal to either of said reference voltage less the input voltage of said amplifier and twice said reference voltage less the input voltage of said amplifier according to the polarity of latter said input voltage; in that connection means are provided for differentially applying said sample and reference voltages to the input of that of said amplifiers which belongs to the first of said cascaded circuits, together with further connection means connecting one of said common points in each one of said cascaded circuits with the input of the amplifier included in the following one of said cascaded circuits, and with still further connection means for connecting the other of said common points in latter said one of said circuits to said linear encoder; and in that each of said amplifiers in said cascaded circuits from the second one on includes differential ingut means fed on one hand from the precedin one of sai circuits and on the other hand rom sai reference voltage.

2. A device as claimed in claim 1 in which at least part of said further connection means include a voltage divider including two series-connected resistors.

3. A device as claimed in claim 1, in which said amplifiers are operational amplifiers. 

1. A device for converting analog signal voltage samples into PCM signals with amplitude compression, comprising: means for successively comparing with a predetermined reference voltage each of said samples and the products thereof by increasing powers of two and for producing from the comparison an encoded binary sequence consisting of binary digits having one predetermined of two possible signalling conditions each time said voltage sample and products are below said reference voltage; means for forming a remainder signal whose amplitude is equal to the difference obtained by subtracting said reference voltage from the lowest of said products which is larger than said reference voltage; a linear encoder for linearity encoding said remainder signal and translating it into a first PCM coded group; a computer for translating said sequence into a second PCM coded group; and means for transmitting the assembly of said first and second coded groups; said device being further characterized in that: said successive comparison means and remainder signal forming means consist of a plurality of cascaded circuits, each of which comprises a differential amplifier having a first and a second negative feedback path, said first negative feedback path including a first diode oriented to conduct from the output to the input of said amplifier and series-connected at a first common point with a first resistor, said second negative feedback path including a second diode oriented to conduct from the input to the output of said amplifier and series-connected at a second common point with a second resistor having either of two resistance values equal to half and twice that of said first resistor according to the even or odd rank of said amplifier in said plurality of cascaded circuits whereby said amplifier delivers at one or the other of said common points a voltage equal to either of said reference voltage less the input voltage of said amplifier and twice said reference voltage less the input voltage of said amplifier according to the polarity of latter said input voltage; in that connection means are provided for differentially applying said sample and reference voltages to the input of that of said amplifiers which belongs to the first of said cascaded circuits, together with further connection means connecting one of said common points in each one of said cascaded circuits with the input of the amplifier included in the following one of said cascaded circuits, and with still further connection means for connecting the other of said common points in latter said one of said circuits to said linear encoder; and in that each of said amplifiers in said cascaded circuits from the second one on includes differential input means fed on one hand from the preceding one of said circuits and on the other hand from said reference voltage.
 2. A device as claimed in claim 1 in which at least part of said further connection means include a voltage divider including two series-connected resistors.
 3. A device as claimed in claim 1, in which said amplifiers are operational amplifiers. 